Oils used as lubrication fluids in internal combustion engines are subject to progressive degradation in use due to exposure to elevated temperatures in an oxidizing environment; high shear stresses; and contamination from combustion products or other sources. Thus the performance of a lubrication fluid is continually reduced during service until its lubricating properties fail to meet minimum specifications and it must be changed or replaced with new oil. While numerous bench-top analytic measures have been shown to correlate with engine oil condition, they require: obtaining a sample of the oil; subjecting the oil to chemical analysis, frequently using sophisticated equipment; and interpretation of the results. These analytic measures are therefore well-suited to research assessments of oil quality but are not a preferred approach for in-service assessment of oil condition.
Extending vehicle engine oil change intervals until the lubrication capability of the fluid meets only minimum acceptable specifications is desirable, both to increase customer convenience and to conserve natural resources. However significantly extending engine oil change intervals requires reliable knowledge of the state of the oil so that the customer may be promptly notified of the need for an oil change when in-service degradation has reduced lubrication performance to minimally acceptable levels.
Manufacturers have responded to this need by either mandating an oil change after a fixed mileage interval or by employing an algorithm based on engine operating conditions which will estimate the remaining oil life and providing the results to the vehicle operator. These indicators are usually specified to underestimate the lubrication fluid life in order to avoid any damage to the engine or other mechanism.
Thus there is need of a more accurate method for determining the useful life of a lubrication fluid.